The Symbiotics... armed with their highly developed physical sciences and with sub-atomic power, they were able to construct, out in space, artificial planets for permanent habitation. These great hollow globes of artificial super-metals, and artificial transparent adamant, ranged in size from the earliest and smallest structures, which were no bigger than a very small asteroid, to spheres considerably larger than the Earth. They were without external atmosphere, since their mass was generally too slight to prevent the escape of gases. A blanket of repelling force protected them from meteors and cosmic rays. The planet's external surface, which was wholly transparent, encased the atmosphere...

As the aeons advanced, hundreds of thousands of worldlets were constructed, all of this type, but gradually increasing in size and complexity. Many a star without natural planets came to be surrounded by concentric rings of artificial worlds.